In recent years, extensive research has been directed to light-emitting apparatuses including a semiconductor light-emitting device, such as a light-emitting diode (LED) or a semiconductor laser (laser diode (LD)), as an excitation light source and a light-emitting element (light emitter) containing a phosphor that emits fluorescence as illumination light when the light-emitting element is irradiated with excitation light emitted from the excitation light source.
An example of the art related to such light-emitting apparatuses is an illumination apparatus disclosed in PTL 1. This illumination apparatus includes a semiconductor laser as an excitation light source to provide a high-intensity light source. Laser light emitted from the semiconductor laser is coherent light with high directivity and can therefore be efficiently collected and utilized. A light-emitting apparatus including a semiconductor laser (hereinafter referred to as “LD light-emitting apparatus”) as an excitation light source is suitable for vehicle headlamps. The use of a semiconductor laser as an excitation light source provides a high-intensity light source that would not otherwise be feasible with LEDs.
If laser light is used as excitation light, the temperature of the light-emitting element, which is extremely small, i.e., has an extremely small volume, is easily raised by the portion of the excitation light, incident on and absorbed by the light-emitting element, that is converted into heat without being converted into fluorescence by the phosphor. This results in degraded characteristics of and thermal damage to the light-emitting element.
To solve this problem, the invention in PTL 2 includes a light-transmissive plate-shaped heat-conducting member thermally connected to a wavelength-converting member (corresponding to a light-emitting element) to reduce the heat generated by the wavelength-converting member.
The invention in PTL 3 includes a cylindrical ferrule holding a wavelength-converting member and a wire-shaped heat-conducting member thermally connected to the ferrule to reduce the heat generated by the wavelength-converting member.
The invention in PTL 4 includes a heat-dissipating member disposed on the side of a light-converting member (corresponding to a light-emitting element) facing semiconductor light-emitting devices and having a passage through which refrigerant flows to cool the light-converting member.
PTL 5 discloses a structure in which a light-transmissive heatsink is thermally connected to a surface of a high-power LED chip used as a light source to cool the high-power LED.